The invention relates generally to the control of chemical reactions by heterogeneous catalysis, and, more particularly, to the control of the catalytic reaction by a surface acoustic wave (SAW) device.
Most catalysts of current use in heterogeneous catalysis contain one or more transition metals which provide active electronic surfaces which stimulate the catalytic action. For single crystals of a transition element, such as platinum, the catalytic reaction is more efficient if the crystal is cleaved along certain crystallographic planes. This indicates that the surface states are a function of the crystallographic plane. These surface states determine the electric field near the metal surface. This electric field controls certain catalytic reactions that take place near the surface.
Most of the transition metals used as catalysts are group 8 elements. In particular, platinum and platinum-type metals, which are relatively rare and costly elements which must be imported from countries such as the U.S.S.R. and South Africa, are widely used in catalytic conversion devices such as fuel cells and in many energy conversions schemes used by the petroleum industry and in chemical processes in general. It would be highly desirable if the quantity of platinum and platinum-like metals required in such catalytic conversion devices could be reduced, or if abundant, inexpensive, group 8 elements such as iron, cobalt, or nickel, could be used in these catalytic conversion devices in Place of platinum or platinum-like elements. Further, it would be highly desirable to eliminate the need of any transition elements in certain heterogeneous catalysis processes.
It is known that the propagation of an acoustic wave along the surface of a piezoelectric material creates an electric field adjacent this surface, and that the intensity and shape of this electric field can be controlled by appropriate doping of the piezoelectric material and by the frequency and intensity of the surface acoustic wave (SAW). Also, it is known to adjust the center frequency of a SAW device by depositing a film of electrically nonconducting material on the surface of the piezoelectric material along which the SAW is propagated, as described in White et al. U.S. Pat. No. 4,243,960, issued Jan. 6, 1981.